Satellite dishes have become very prominent in today's society. Many people use them to receive television signals directly. This eliminates the need, for example, for cable connections between homes and television service providers. One problem with these satellite dishes is their size. Big satellite dishes can be an eyesore on a homeowner's property.
When constrained to use a small dish reflector, typically 18 inches in diameter, another problem develops. This problem is that the amount of power that is focused to the feed horn is small relative to a much larger dish. In general, the smaller the dish, the fewer electromagnetic waves collected by that dish and focused to the feed horn. The fewer electromagnetic waves that are focused to the feed horn, the lower the signal's power that is transmitted to the feed horn.
This problem of low power becomes exacerbated during cloudy, stormy, or otherwise inclement weather--a problem referred to as "rain fade." As the electromagnetic waves are propagating from the satellite to the individual satellite dishes, clouds or other water or the like, or other atmospheric disturbances can absorb or reflect some of the radiation. Thus, for example, on a rainy day, using a small dish, the signals reflected to the feed horn may become too weak to provide proper reception. In the television example, this can result in the picture freezing, breaking into parts, or being entirely lost until the interference decreases.
The primary source of interference from rain fade is from raindrops or other forms of moisture or particles in the atmosphere between the satellite and the dish. Water, for example, absorbs microwave energy, so increased amounts of water in the atmosphere between the dish and the satellite increase the likelihood of interference with reception. Thus, heavy cloud cover absorbs a small amount of the energy, really heavy cloud cover absorbs a large amount of energy, and rain dropping through the atmosphere typically absorbs an even greater amount of energy.
The variation in signal strength resulting from rain fade may be seen during rain events by observing a signal strength meter. Many systems for satellite reception include an on-screen signal strength meter that may be viewed, for example, on a television screen. During a rainstorm, it has been experimentally determined that signal loss generally occurs with a typical existing 18-inch Digital Satellite Systems (DSS) satellite dish system at approximately 20% to 30% aperture efficiency, which is typically called "signal strength" level in on-screen guides.
Once the signal falls below about 30%, the digital system used with satellites typically loses the signal completely, and, for a television, no picture at all is received. This loss of picture occurs, depending on the part of the United States or other part of the world in which the receiver is located, for example, between one-tenth of one percent to four-tenths of a percent of the time. It has also been estimated that an average of 24 hours of lost signal per year occurs for a typical satellite system installed in the United States. This problem is particularly annoying to viewers when the signal is lost when they have paid for a pay-per-view movie or are entertaining guests or customers (e.g., bar customers watching sporting events). People who buy these types of satellite receivers typically have made a significant investment in the system and programming, and expect reliable performance. As a result, there is a need for a simple, relatively inexpensive solution to the problem of rain fade.
One known approach to addressing rain fade is to attempt to block rain from collecting on the antenna dish reflector itself. For example, SGard Incorporated of Pocahontas, Ak. provides an extension or hood mounted perpendicular to the face of and above the rain reflector so as to prevent such rain collection. This device appears to have received Design Patent No. 400,888. A problem with this approach is that it only addresses reduced signal resulting from collection of rain on the reflector surface itself. Generally, the maximum signal attenuation resulting from distortion of the dish surface caused by rain collection and splashes is much less than the attenuation caused by water in the atmosphere that interferes with reception.
It is also known in the art to provide three part antennae, which include two extensions for circular transmission antennae, such as those used for vehicle-mounted communications antennae. U.K. Patent Application No. 2167904A of Butcher describes such an antenna. The invention of Butcher provides for extension of the parabolic surface of the dish used by such transmitters and receivers, but does not address a number of problems for small television or the like signal receivers. For example, the invention of Butcher does not address the problem of additional wind resistance and other stresses of the extensions to the dish. The invention of Butcher also does not address shape requirements for small dishes, which typically have offset feed horn collectors placed near the lower part of the antenna and reflectors that cover only the upper portion of possible parabolic reflector area, while also addressing the problem of collection of rain, debris, or other matter on the antenna reflector surface. The invention of Butcher is also not easily installable. The Butcher invention further fails to address the likelihood of a mismatch between the new dish shape and the illumination pattern of the transmission feed horn. Thus, the added "wings" on the dish do not reflect significant energy that can be collected by the feed horn in satellite dish applications and the modification has very limited utility.
An article in April 1992 IEE Proceedings-H titled "Compound Reflector Antennas," by Lee et al. describes a compound reflector antenna for reflecting equal beamwidths at two separate frequency bands using inner and outer reflective surfaces of differing materials. The article of Lee does not describe reflector extensions for use with small satellite dishes to increase gain, nor does it address particular aspects of adapting reflector extensions to existing dishes, particularly smaller satellite dishes. The article also does not address the need to alter the location of the feed horn to place it at the focal point of the extended reflector.
U.S. Pat. No. 3,631,504, issued to Suetaki et al. shows an antenna having a parabolic reflector that includes a wave absorber at its edge. The '504 patent does not describe reflector extensions for use with small satellite dishes to increase gain, nor does it address particular aspects of adapting reflector extensions to existing dishes, particularly smaller satellite dishes. The patent also does not address the need to alter the location of the feed horn for use with an extended reflector.
U.S. Pat. No. 5,298,911, issued to Li shows an antenna having a skirt at its rim, the skirt having a serrated surface and rolled curvature to control amplitude and phase taper of the transmnitting or receiving radiation. The '911 patent does not describe reflector extensions for use with small satellite dishes to increase gain, nor does it address particular aspects of adapting reflector extensions to existing dishes, particularly smaller satellite dishes. The patent also does not address the need to alter the location of the feed horn for use with an extended reflector.
U.S. Pat. No. 5,456,779, issued to Sinha relates to a method for attaching an electrically conductive mesh material to an antenna structure for use as a high performance radio frequency reflective surface. The '779 patent does not describe reflector extensions for use with small satellite dishes to increase gain, nor does it address particular aspects of adapting reflector extensions to existing dishes, particularly smaller satellite dishes. The patent also does not address the need to alter the location of the feed horn for use with an extended reflector.
Larger replacement satellite dish antennae are available in the aftermarket for consumers, but these have achieved very small market penetration, as they require time consuming and difficult installation and dish pointing which is daunting to most dish owners. Some owners of existing installed dishes have a need to replace these dishes with new dishes offering additional features.
There is thus a need for an easily installable and cost-effective device for increasing the reflective power of a dish for a received signal transmission to overcome rain fade and other signal interference without significantly increasing vulnerability to wind damage or other sources of stress and without producing the problem of creating additional reflective surface that may collect rain, snow, debris, or other matter, thus interfering with the received signal. There is also a need for a simple method for using an installed dish to pre-aim a new dish. There is yet another need for an easy method of installing a dish with additional features (such as the ability to pick up signals from two satellite locations at once) by using an existing installed dish as an aiming reference.